1. Field of the Invention
The invention relates to a method of depositing epitaxial monocrystalline layers in accordance with sliding liquid phase epitaxy and somewhat more particularly to such a method wherein a plurality of substrates are substantially simultaneously provided with multiple epitaxial semiconductive layers.
2 Prior Art
In the production of certain specific semiconductor components, for example, luminescent diodes or laser diodes, it is necessary to epitaxially deposit one or more layers of a semiconductive material on a substrate, such as a semiconductor crystal. Particularly, in the production of semiconductor components composed of intermetallic III-V compounds and their mixed crystals, the technique of sliding liquid phase epitaxy is typically utilized.
Generally, in this method a melt containing the semiconductive material to be deposited is moved onto a surface of a substrate with the aid of a slider or the like and the material is deposited on such surface in a monocrystalline condition by subjecting the arrangement to a slight cooling. As soon as a desired thickness of the monocrystalline layer is obtained via such deposition, the residual melt is removed or pushed-off from the substrate surface or from the newly formed epitaxial layer with the aid of the slider means. Such a sliding liquid phase epitaxial technique and an arrangement for practicing such technique are described, for example, in U.S. Pat. No. 3,753,801.
In order to produce coherent and incoherent radiating double heterostructured diodes, for example, of a (Ga, Al) As-GaAs diode or microwave elements having a heterostructure, it is necessary to epitaxially deposit a plurality of layers one on top of the other on a given substrate. These layers differ from one another in their respective compositions, for example, in a GaAs-GaAl-As layer sequence, such layers may differ in the aluminum concentration within the various layers.
Layer sequences such as are, for example, required for double heterostructure laser diodes or luminescent diodes, are normally produced with suitable sliding equipment in which substrate discs are located in suitably designed indentations or recesses within a so-called furnace "boot", generally composed of graphite, which is operationally associated with a moveable slide member having a plurality of melt-receiving chambers for receiving melts of different compositions. In this type of equipment, the substrate discs are consecutively, in a linear or concentric manner, spaced a select distance from one another in the boot and the melt-receiving chambers of the slide member are also consecutively spaced from one another. By linearly sliding or concentrically turning the slide member, the respective melts are consecutively moved across the respective substrates and a monocrystalline epitaxial layer grows on the substrate surfaces when the melt is cooled by a specific amount. The thickness of a so-grown layer is generally determined by the magnitude of the temperature drop of the melt and by the thickness of the melt over the substrate. Further, as long as a controlled temperature drop occurs within the melt containing the materials or compounds being epitaxially grown, the thickness of the so-grown layers is also determined by the rate of cooling the melt the desired amount. If extremely thin layers are to be deposited on a substrate, melts must be utilized for the deposition process which are saturated with the material forming the substrate so that an uncontrolled dissolving of the substrate material at the surface of the substrate does not occur, which would cause an uncontrolled layer growth. A precise saturation of the melt is most readily produced in a respective melt by a dissolving or compositional material balance between the melt and the material of the substrate, for example by providing a sufficiently long contact time between a "pre-substrate" (composed of an identical material as the substrate) and the melt before the actual substrate is moved into the growth position. In apparatuses where several substrate discs are to be simultaneously provided with a multi-layered structure, a separate recess must be provided in the sliding means for each substrate disc along with a separate chamber for each layer to be deposited. Thus, for example, in order to produce a four-layered structure on a substrate in which respectively different cooling intervals must be utilized in order to deposit individual layers, a slider must be provided having a sufficient number of individual chambers to correspond to four times the number of substrate discs to be layered. Clearly, this leads to very complicated constructions of the slide or of the "boot", even with relatively small number of substrate discs. Additionally, the relatively large chamber number in such a device could easily lead to serious mistakes in loading such "boots". Finally, because of the necessity of "pre-substrates" via this technique, the number of substrate discs is doubled and, necessarily, additionally increase the cost of the overall process.